The present invention relates to a request buffer apparatus which is adopted in a data processing system in which a plurality of independent devices (e.g., main memories) are commonly used for various pieces of equipment, and which controls requests from these various pieces of equipment.
A conventional request buffer apparatus of this type has a "First-In-First-Out" (FIFO) request buffer. Thus, requests (memory bank access requests) from the various pieces of equipment to a plurality of memory banks are stored in the request buffer in the order in which they are received. A control device of the request buffer monitors the ready/busy state of each memory bank. When a memory bank is ready (accessible), the control device determines if the first request stored in the request buffer is a request to this memory bank. If so, the first request is produced from the request buffer, thereby allowing accessing to the memory bank. On the other hand, if the memory bank is busy, the output of the initial request is withheld until the memory bank is ready. In this manner, in a conventional request buffer apparatus, requests from various pieces of equipment are produced in the order in which they are received when the corresponding memory banks are ready, thereby allowing accessing to the memory banks. For this reason, even if a memory bank corresponding to a request stored in the request buffer is ready, if another request to another memory bank which was received prior to the former request is also stored in the request buffer, execution (memory bank access) of the former request is withheld. As a result of this, in the conventional system, the waiting time within the request buffer becomes long, and this lowers the overall processing speed.
Meanwhile, it is also known to arrange a plurality of request buffers in correspondence with a plurality of memory banks, such that each request buffer stores only requests to the corresponding memory bank. However, although the problem of a low processing speed as described is solved, the amount of hardware inevitably increases.